1. Field of the Invention
The present invention relates to heavy lids for subsurface enclosures, and particularly for lids on pits designed for use in servicing aircraft, etc. at docking, loading and refueling terminals.
2. Description of the Prior Art
At modern aircraft terminals servicing of aircraft on the ground is frequently performed using prefabricated pits which are installed at aircraft docking, fueling and loading areas beneath the surface of the tarmac across which aircraft travel during docking and departure maneuvers. The pits are typically formed of fiberglass, steel or aluminum and are constructed as enclosures with surrounding walls, a floor, and an access lid at the top of the walls. The pits are installed below the surface of loading and refueling aprons at aircraft terminals, remote parking locations and maintenance bases.
The purpose of the pits is to allow ground support functions to be carried out from subsurface enclosures. These ground support functions include the provision of fuel, the provision of electricity to the aircraft while it is in the docking area, the provision of air for cooling the aircraft interior and pressurized air for starting the aircraft engines, and other aircraft support activities on the ground. The use of subsurface pits eliminates the need for mobile trucks, carts and other vehicles which are otherwise present in the loading area and which interfere with the arrival and departure of aircraft in the vicinity of a loading gate. The use of subsurface pits also allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with great efficiency at a central location, as contrasted with mobile generating or supply vehicles.
The pits located below the aircraft terminal area house valves, junction boxes, cooling air terminations and other terminal equipment used to service an aircraft that has been docked. Umbilical pipes and lines, otherwise housed within the pits, are withdrawn from the pits through hatches therein and coupled to the docked aircraft to supply it with fuel, air for cooling the aircraft interior, pressurized air for starting the engines, and electrical power.
The pits are constructed with hinged, disc-like hatches within a more expansive, generally rectangular lid. The hatches are ordinarily used to withdraw fueling lines and the like, and can be lifted using one hand. Both the hatches and lids must be constructed of heavy-duty aluminum or steel, or other material, as they must be able to withstand the weight of an aircraft as it rolls across the surface.
Conventional pit lids are far too heavy to be lifted manually, even though it is quite desirable to have access to the complete enclosure of the pit for servicing faulty equipment, freeing fouled lines, and for performing other maintenance and repair functions in the pit. Heretofore, it has been necessary to employ a motorized lift or other machine to raise the lid of a subsurface pit for this reason. Pits of the type described are constructed in various sizes, and lids having dimensions of four to eight feet by three to five feet are typical. Accordingly, a very large force is required to lift such a lid.